Fuel cell system

Abstract

A fuel cell system is provided that can suppress the degradation of the MEA and simultaneously assure the merchantability. The fuel cell system 1 includes: a fuel cell 10 that generates electric power by reacting hydrogen gas and oxidant gas; a temperature sensor 103 that detects the temperature of the fuel cell 10; a voltage lower limit calculation portion 31 that sets the voltage threshold to limit the output of the fuel cell10 based on the temperature detected of the fuel cell 10; a current upper limit calculation portion 32 and the current limiting portion 33 that limits the output of the fuel cell in a case where the voltage generated by the fuel cell 10 is lower than the voltage threshold.

Description

[0001]This application is based on and claims the benefit of priority from Japanese Patent Application No. 2007-147422, filed on 1 Jun. 2007, the content of which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to a fuel cell system. In particular, it relates to a fuel cell system mounted to an automobile.[0004]2. Related Art[0005]Recently, fuel cell systems have drawn attention as a new power source for automobiles. The fuel cell system includes, for example, a fuel cell that generates electric power by chemically reacting reactant gas, a reactant gas supplying device that supplies a reactant gas to the fuel cell via the reactant gas channel and a control device that controls the reactant gas supplying device.[0006]The fuel cell has, for example, a stack structure in which several tens to several hundreds of cell are laminated. Each cell is configured by sandwiching a membrane electrode assembly (MEA) by a p...

AI Technical Summary

Benefits of technology

[0013]The object of the present invention is to provide a fuel cell system that can suppress the degradation of the MEA and at the same time assure the merchantability.

[0015]According to the present invention, the voltage threshold value is set based on the fuel cell temperature. The output of the current and the power, etc. of the fuel cell is limited by this voltage threshold value. Therefore, as the voltage threshold value is set according to the temperature characteristics related to MEA degradation, the performance degradation of the fuel cell by the excessive limitation of the output can be avoided. As a result, the discomfort arising from degradation in drivability can be avoided and the merchantability can be assured.

[0016]Moreover, as the voltage threshold value is set based on the fuel cell temperature, the cell voltage entering into the MEA degradation range can be avoided even in a case where the fuel cell temperature changes.

[0018]According to the present invention, the output limiting value is determined by the voltage threshold value according to current versus voltage characteristics showing the relation between the generated current and the generated voltage so that the output limiting value can be reliably determined.

[0020]According to the present invention, the fuel cell system sets the current threshold value based on the fuel cell temperature and limits the output of the current and the power, etc. of the fuel cell by this current threshold value. As is described, by setting the current threshold value according to the temperature characteristics related to the MEA degradation, a similar effect can be expected as described above.

[0024]According to the present invention, the fuel cell system sets the voltage threshold value or current threshold value in the low temperature range in which the voltage condition becomes severe to suppress the MEA degradation such as while warming up. Here, as the temperature characteristics related to the MEA degradation and the current versus voltage characteristics become stable in the temperature range after the warming up period, it is no longer necessary to set the threshold value according to the temperature, and then a constant output limit can be executed. Consequently, according to the present invention, after the warming up period, the load can be reduced of processing the output limitation.

Problems solved by technology

Therefore, for example, when the fuel cell is driven in the lower temperature state, the voltage lower limit becomes higher than the specified threshold value and there is a danger of entering the degradation range, despite the cell voltage being higher than the threshold value.

When the threshold value is set high, the voltage lower limit may become largely lower than the threshold value so that the MEA is protected excessively, thereby degrading the drivability.

As described above, it was difficult to keep the compatibility between the merchantability and the protection of the MEA.

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